An average actor, (according to the SAG?) makes scale. What is scale? Is it hourly pay? paid per picture? Are there any residuals? Benefits? Retirement?
Well, without narrowing it down slightly, this is an extremely broad topic as there is no specification as to what type of actors, locations, etc. I will address this from the point of view of SAG-AFTRA, the Screen Actors Guild union in the United States.
For example, SAG-AFTRA has rate sheets available on their website that spell out the hourly rate for various elements of actors. This one, for example, is the pay sheet for Background Actors, in LA, Vegas, Hawaii, San Francisco, San Diego and Sacramento. It further breaks it down into General, Stand In, Photo Double, Omnies and Special Ability. Each of these have their own assigned day rates.
As far as retirement, there is a retirement/pension plan available at SAGPH, and it is based on credits earned, and total money earned. I don't know the specific formula to be able to give a number. Another rate sheet spelled out a 16% retirement benefit, but it was unclear if that was over and above the day rate, or taken out of pay earned.
As far as residuals and per picture, those are generally reserved for "billed" or otherwise main/minor character, and would be negotiated as part of the contract. Some stars will give up some compensation for better billing, or vice versa, or some combination of all of the above. Background/extra characters would be the ones receiving scale wages.
So while a rough outline can be given, no exact figures unless you have a specific incidence in mind, such as a radio spot with a 13 week airplay in the NY/LA zones, two members involved. (Yes, the sheets get into that much detail.)